Abstract: Fertilizer reduction and efficiency have become key issues for sustainable agricultural development. This study focused on the effects of a moderate reduction in phosphorus fertilizer application on the physiological characteristics and material production capacity of potato leaves with the aim of exploring effective ways to enhance potato yield and economic benefits. In 2018−2019, a phosphorus fertilizer reduction experiment with different application gradients was set up in Dazui Village, Haiyuan County, Ningxia, with the customary phosphorus application by local farmers (240 kg·hm⁻², RP) as the relative control. Four phosphorus reduction treatments were set up: P25 (180 kg·hm⁻², 25% reduction), P50 (120 kg·hm⁻², 50% reduction), P75 (60 kg·hm⁻², 75% reduction), and CK (0 kg·hm⁻², no phosphorus fertilizer as the absolute control), to systematically monitor the changes in the functional indices of the leaves and the characteristics of the dry matter accumulation in potato and to analyze the correlations between these changes and the yield and economic benefits. Adequate phosphorus reduction could effectively optimize the functional characteristics of potato leaves, with the P50 treatment having the best effect. Specifically, leaf area index (LAI), net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), chlorophyll a (Chla) content, chlorophyll b (Chlb) content, and carotenoids (Car) content were increased by 34.39%, 8.28%, 5.39%, 30.27%, 30.75%, 25.08% and 28.80%, respectively, in the P50 treatment compared with those in RP, and the arrival of leaves at the onset of senescence was delayed by 2.26 d. This treatment also significantly increased the antioxidant capacity and levels of osmotic regulating substances in potato leaves and inhibited the expansion of cellular membrane permeability and the accumulation of malondialdehyde (MDA). Simultaneously, the maximum dry matter accumulation rate (G_max) and average accumulation rate (G_mean) were significantly increased. The potato yield of the moderate phosphorus reduction treatments did not decrease owing to the reduction in phosphorus fertilizer dosage, and some treatments, even increased fertilizer at P50, performed the best, followed by P25. Principal component analysis showed that the composite scores for all treatments were in the order of P50>P25>RP>P75>CK. Phosphorus reduction 50% (120 kg·hm⁻², P50) improved the physiological characteristics of potato leaves and optimized the dry matter accumulation characteristics compared with that of the other treatments, and could maximize the potato yield and commercial potato yield. Therefore, phosphorus application of 120 kg·hm⁻² can be considered as the recommended phosphorus application rate for reducing phosphorus use and increasing the efficiency of potato in the semi-arid region of Northwest China, so as to achieve the purpose of green and high-yield cultivation.